1. Field of the Invention
The present invention relates to a computer system control method, a computer system, and storage device control method and in particular, to a method for controlling information processing system which creates a virtualized volume snapshot, a computer system and storage device control method and a storage device.
2. Description of the Related Art
In information processing system installed in banks and stock companies, online processing and batch processing may be terminated abnormally by a program bug or storage device failure and any contradictions may occur in data. Moreover, data may be erased by a careless mistake of an operator of an information processing system. To eliminate the data contradiction and resume the processing which has stopped in the middle or to restart the processing which has stopped in the middle, it is often a case that backup operation is performed as a routine work.
As a conventional technique of this type, for example, a technique disclosed in JP-A-2000-132343 is known. This conventional technique is related to a storage device system in which to obtain backup for a copy of data without preventing access to the data to be backed up, a frozen image copy (snapshot) with data consistency can be created. In this conventional technique, a snapshot is created not in a host computer but in a storage device system, so as to reduce the load of the host computer accompanied by a snapshot formation such as data copying. In this conventional technique, the storage device system creates a snapshot as follows. Data copying is performed between a copy source (source) volume and a copy destination (destination) volume specified by a host computer and a copy stop for freezing data (division of a volume pair) and data resynchronization are controlled on volume unit basis. Furthermore, in this conventional technique, in order to reduce data copy quantity so as to reduce the time required for copy and the processing load, the data copy, division, resynchronization and the like are performed only for a necessary region within the volume.
Use of the aforementioned snapshot is effective not only for the backup but also for the data transfer and the data sharing with data consistency between the databases.
Moreover, recently, in the information processing systems, an enormous data quantity is used and there arises a problem that cost for managing a storage device and a storage region has become very high. Concerning this, a research company Moregan Keegan has reported “Virtualizing the SAN” (Jul. 5, 2000). According to this report, a physical volume provided by a storage device is flexibly virtualized according to a request from a host computer, and this virtualized volume is supplied to the host computer, thereby enabling reduction of the management cost. Furthermore, the report shows an example of several system configurations and methods for virtualization.
One of them is as follows. A server for virtualization is connected between a host computer and a storage device system and the server address-converts one or more physical volume regions for the host computer, thereby creating a virtualized volume, so as to manage correspondence between a physical volume region and a virtualized volume region. An access to the virtualized volume by the host computer is converted into an access to the physical volume, thereby processing an access request by the host computer. Moreover, in another example, a host computer is connected to a storage device system and further server is connected to the host computer for managing correspondence between a physical volume region and a virtualized volume region. When the host computer accesses the virtualized volume, the request for accessing the virtualized volume by the host computer is received by access processing software on the host computer and the software asks the server about a position of data to be accessed on the physical volume. The server replies the position to the software and the software accesses the physical volume provided by the storage device system by using the position, thereby processing the access request of the host computer.
Each of the aforementioned two examples has means for maintaining information of correspondence between a physical volume region and a virtualized volume region and managing correspondence between the physical volume region and the virtual volume region.
Moreover, the correspondence between the physical volume and the virtualized volume may be one of the following three cases: a region constituting one virtualized volume is contained in only one physical volume; a region constituting one virtualized volume is contained in a plurality of physical volumes; and regions constituting a plurality of virtualized volumes are contained in only one physical volume. Moreover, a plurality of physical volumes may belong to different storage device systems.
In the aforementioned conventional technique in which a storage device system creates a snapshot, management of a source volume and a destination volume and control of data copy, division, resyncrhonization have been performed according to a physical volume provided by the storage device system. For this, when a storage region is virtualized as has been described above, the aforementioned conventional technique has a problem that when creating and using a snapshot according to a virtualized volume used by a host computer, a limit is caused in control of the snapshot. For example, when regions constituting a plurality of virtualized volumes are at least partially contained in one physical volume, in order to create a snapshot of the aforementioned virtualized volume, it becomes necessary to create a snapshot about the aforementioned physical volume. As a result, a destination volume of the physical volume contains both of the virtualized volumes and operation of the snapshot of one of the virtualized volumes may affect the other and it is impossible to perform control such as division and resynchronization for snapshot of each of the virtualized volumes independently from each other.
Moreover, when a region constituting one virtualized volume is contained in a plurality of physical volumes, formation of snapshot of the virtualized volume requires formation of snapshot of the plurality of physical volumes. However, since the snapshot formation instruction and control instruction to the storage device system are performed on physical volume basis, snapshot formation for one virtualized volume requires instruction including timing synchronization about the respective physical volumes a plurality of times. This complicates the snapshot management and control, increasing the processing overhead.